A. Field of the Invention
The present invention relates to a vented closure assembly for a containing structure, such as a milk tank.
B. Brief Description of the Prior Art
In the dairy industry, milk is commonly transported from dairy farms to a central processing center by means of tank trucks and trailers. The milk-containing tank itself is generally made of stainless steel and is commonly of a double-walled construction with insulation between the inner and outer stainless steel walls, so that the contained milk can be kept at an adequately low temperature while being transported.
Because of the sanitation requirements of the dairy industry, the interior of the milk tank must be thoroughly washed at regular intervals. Also, it is necessary to provide the tank with an access opening, commonly called a "manhole," to permit an inspector to actually enter the interior of the tank. Obviously, while milk is being transported, this access opening must be properly covered both to prevent milk from being spilled out the opening, and also to prevent outside contaminants from being mixed with the milk. There is a further requirement that the interior of the tank be vented to the outside atmosphere, since with an airtight tank even small temperature variations in the milk would cause undesired pressure differentials between the area inside the tank and the surrounding atmosphere.
A quite common means of providing the venting in a milk tank is to provide a venting member in an interior metal cover which normally closes the access opening of the tank. This venting member generally comprises a cylindrical tube mounted to the center of the cover and extending downwardly toward the interior of the tank. The interior of the tube is provided with a set of vertically spaced, staggered baffles which overlap sufficiently to define a circuitous passageway from the interior to the exterior of the tank. An annular gasket member made of a flexible material is usually placed between the perimeter portion of the cover and the support ring which defines the tank access opening, to provide a perimeter seal. Also, an exterior dust cover is positioned over the interior cover. The sanitation standards of the dairy industry require that all components which possibly come into contact with the milk be thoroughly cleaned at regular intervals.
While the prior art closure assemblies have been able to perform the closing and venting functions for a milk tank in a manner to meet the standards of the dairy industry, there is a continuing need for improvement, with regard to such things as simplicity of structure, ease and reliability of operation, capability of being thoroughly cleaned, and low cost of initial fabrication, as well as low cost in operation and maintenance. It is an object of the present invention to provide an improved closure assembly for a milk tank or the like, which incorporates a desired balance of advantageous features, with regard to the factors indicated above.